The objective of this proposed research is to continue to develop and maintain special recombinant inbred strains of mice, and to use these stocks in the genetic analysis of the manifold qualitative and quantitative differences that distinguish inbred strains of mice. Thus, the emphasis will be on traits analogous to those that differentiate individuals who are free from major genetic diseases. These include such conditions as late onset disease, chronic conditions, and diseases that depend upon genotype-environment interaction for manifestation. Examples of such traits are late onset diabetes, allergies, and drug induced anemias. One or more of these infirmities affects nearly everyone, yet they are compatible with survival and reproduction. Qualitative differences (polymorphisms) that have no known functional significance also will be studied. These will serve as the essential genetic markers for analysis of the variations with functional significance. For any one trait, formal knowledge will be obtained about the number of loci involved, their locations in the linkage map, and their epistatic relationships. This formal genetic knowledge will be used to develop and test hypotheses concerning function.